This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This was a pilot project that supported the development of a rhesus macaque model of monkeypox virus (MPV) infection and disease. The goal was to characterize the disease course and host response to MPV infection as this had not been well characterized. During the study period, we found that animals inoculated intrabronchially with the Zaire strain of MPV exhibited clinical symptoms consistent with smallpox. Specifically, these animals exhibited widespread pox lesions, which were coincident with elevated temperatures. Immunologically, these animals exhibited robust T and B cell proliferative responses following inoculation that lead to CD4 and CD8 specific T cell responses as determined by intracellular cytokine staining. Having characterized the virological parameters and the host response to infection, we initiated comparative infection studies to define potential phenotypic differences between wild type MPV and targeted mutants of MPV. We started with a recombinant that lacks the monkeypox inhibitor of complement enzymes (MOPICE), a protein widely considered to be a virulence factor for central African strains of MPV. We compared clinical disease and host adaptive immune response following infection with MPXV-Zaire, or recombinant MPXV-Zaire lacking expression of MOPICE. Interestingly, the loss of MOPICE expression results in enhanced viral replication in vivo, as well as a dampened adaptive immune response against MPXV. Taken together these findings suggest that MOPICE plays an important role in the generation of the anti-MPXV immune response, and that this protein is not the sole virulence factor of the Central African clade of MPXV. During the past year we evaluated the pathogenic potential of a recombinant MPV that lacks the viral encoded complement binding protein (vCBP), a protein widely considered to be a virulence factor for central African strains of MPV. This recombinant MPV will enable us to definitively determine if vCBP is necessary for MPV-associated disease. This provides a unique tool to define whether circulating monocytes in MPV-infected animals presenting with monocytosis are MPV-infected.